Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
  Case Tag  
Price  
Sales  
Tax %  
Raw Total  
Incl. Sales Tax  
Rounded  
to Penny  
Rounded  
to Nickel  
Rounded  
to Dime  
  Purchase #1 $61.53   6.416%   $65.4778   $65.48   $65.50   $65.50  
  Purchase #2 $226.62   12.522%   $254.9974   $255.00   $255.00   $255.00  
  Purchase #3 $62.30   4.713%   $65.2362   $65.24   $65.25   $65.20  
  Purchase #4 $234.43   5.109%   $246.407   $246.41   $246.40   $246.40  
  Purchase #5 $9.47   3.714%   $9.8217   $9.82   $9.80   $9.80  
  Purchase #6 $44.67   8.653%   $48.5353   $48.54   $48.55   $48.50  
  Purchase #7 $163.77   8.263%   $177.3023   $177.30   $177.30   $177.30  
  7 purchase totals = $802.79       $867.7777   $867.79   $867.80   $867.70